2008 Annual Report
Beet necrotic yellow vein virus (BNYVV) which causes rhizomania , and its vector, the soil-borne fungus, Polymyxa betae, were detected for the first time in the Western Hemisphere by the Salinas Virology Lab. Research on BNYVV and related viruses has been critical to understanding of the disease and facilitating development by the lab of highly specific and sensitive diagnostic assays. Results from studies of soil-borne sugarbeet viruses led to taxonomic reclassification of some viruses. The laboratory recently described a new strain of BNYVV that overcomes Rz1 gene resistance, that differs from other resistance-breaking (RB) strains by having only the standard 4 RNAs, rather than a fifth as is present in RB strains from Europe and Asia. Recent work by the Salinas Lab has linked the RB trait to amino acid changes in RNA3. The Salinas lab has also described two other soilborne viruses of sugarbeet (BSBMV and BOLV) that compete and interact with BNYVV under field conditions. Additional studies have genetically characterized soilborne viruses of lettuce associated with the diseases, lettuce dieback (two tombusviruses, one described by ARS Salinas) and lettuce big vein (Mirafiori lettuce big vein virus; MLBVV), and examined epidemiological factors contributing to control and spread. Collaborative efforts with sugarbeet and vegetable breeding programs in Salinas have facilitated development of genetic resistance to all three soilborne viruses (BNYVV, Tombusviruses and MLBVV).
Curly top, transmitted by the beet leafhopper (Circulifer tenellus) and caused by Beet curly top virus (BCTV) and related curtovirus members of the genus, Curtovirus, has impacted yields of sugar beet and vegetables since the late 1800s. The Salinas lab has identified crop and weed reservoirs, characterized changes in curtovirus population structure and determined this is likely influenced by environmental and cropping changes, and is developing novel methods for control.
This relates to NP 303, Component 4.
6. Geographical and biological variation among curtovirus species affecting sugarbeet in the western United States. Losses due to curly top in sugarbeet have been increasing throughout the Rocky Mountain production region in recent years, suggesting the possible emergence of a new severe curtovirus species or strain. Sugarbeet plants exhibiting curly top symptoms were collected from throughout not only this region, but all affected sugarbeet production regions, and genus-specific and species-specific PCR primers were used for amplification and sequencing of viral genomic regions previously shown to be reliable for species differentiation. Sequence comparisons among isolates demonstrated that the dominant species have not changed substantially since a previous survey in the mid-1990s, but sequence conservation and divergence analysis indicated 3 different introductions to the U.S. based on differences in conservation within isolates of each of the 3 predominant species. This work illustrates that factors other than emergence of a new species is responsible for increasing disease problems, and clarifies curtovirus epidemiology. This project is a collaborative effort between the USDA-ARS Virology Lab in Salinas, and the NWISRL Pathology Lab in Kimberly, ID, and supports NP303 Component 2, Biology, Ecology, Epidemiology, and Spread of Plant Pathogens and Their Relationships with Hosts and Vectors, Problem Statement 2C: Population Dynamics, Spread, and Epidemiology of Pathogens. 7. The Suppression of resistance-breaking Beet necrotic yellow vein virus isolates by Beet oak-leaf virus in sugar beet. Rhizomania, a serious disease of sugar beet (Beta vulgaris), is caused by Beet necrotic yellow vein virus (BNYVV), and the resistance allele Rz1 has been widely incorporated into commercial cultivars. Recently, resistance-breaking isolates of BNYVV (RB-BNYVV) were identified and characterized from throughout the sugar beet growing areas in the United States, and most soil samples and plants contained Beet oak-leaf virus (BOLV) as well as RB-BNYVV. Plants grown in soils infested with aviruliferous P. betae or carrying RB-BNYVVand BOLV, alone and in combination, were compared with plants grown in noninfested soil for differences in plant fresh weight and virus content to determine if interactions occur between these two viruses. Rz1 and Rz2 resistance genes that condition resistance to BNYVV did not confer resistance to BOLV, and results indicate that BOLV may suppress BNYVV in mixed infections. This work is important toward understanding factors influencing the ability of BNYVV to overcome sources of resistance as well as understanding factors contributing to rhizomania of sugarbeet. All research described above is being conducted by the USDA-ARS Virology Lab in Salinas, in support of NP303 Component 2, Biology, Ecology, Epidemiology, and Spread of Plant Pathogens and Their Relationships with Hosts and Vectors, Problem Statements 2A: Pathogen Biology, Virulence Determinants, and Genetics of the Pathogen, and 2C: Population Dynamics, Spread, and Epidemiology of Pathogens. 8. Release of C812-41 and C812-41CMS Sugarbeet Germplasms with Resistance to Resistance-Breaking Strains of Beet Necrotic Yellow Vein Virus (RB-BNYVV). There is a need to develop sugarbeet germplasm with resistance to RB-BNYVV. Sugarbeet germplasm lines C812-41 and C812-41CMS were developed jointly by the Sugarbeet Breeding and Plant Virology Labs at the USDA-ARS in Salinas and released. C812-41 and its cytoplasmic male sterile counterpart have resistance to RB-BNYVV that causes the severe disease rhizomania. Resistance to RB-BNYVV was introgressed from wild beet Beta vulgaris subsp. maritima into monogerm C812-41, and although not yet confirmed, is suspected to be the Rz2 gene originating from WB42. This resistance was discovered in the germplasm enhancement program at Salinas and confers resistance to RB-BNYVV that defeats widely used Rz1. These germplasm resources represent ongoing efforts to combine multiple disease resistance with high productivity and to enhance source populations with genes from wild beet accessions, and this germplasm line will give the sugarbeet seed industry and ultimately the growers and processors an additional source of resistance to rhizomania. The virology research described above was conducted in support of NP303 Component 2, Biology, Ecology, Epidemiology, and Spread of Plant Pathogens and Their Relationships with Hosts and Vectors, Problem Statement 2A: Pathogen Biology, Virulence Determinants, and Genetics of the Pathogen. 9. Specific polyclonal antibodies prepared against recombinant coat protein of Pelargonium zonate spot virus and immunodetection. Pelargonium zonate spot virus (PZSV) was identified in U.S. tomatoes in 2006, with infected plants showed stunting, malformation, yellow rings and line patterns on the leaves and concentric chlorotic ringspots on the stems. The coat protein (CP) gene of a California isolate of PZSV was amplified using primers designed to a published sequence, the amplified gene was cloned into an expression vector, with the resulting expressed protein tagged with 6xHis at the N-terminus. Recombinant CP, detected in the insoluble fraction, was purified and used to raise polyclonal antibodies. Crude antiserum was successfully used in indirect ELISA and Western blots to detect PZSV in infected tomato leaves as well as on a wide range of hosts, which will be of benefit in monitoring for this emerging tomato virus in tomato and other hosts. All research described above is being conducted by the USDA-ARS Virology Lab in Salinas, in support of NP303 Component 2, Biology, Ecology, Epidemiology, and Spread of Plant Pathogens and Their Relationships with Hosts and Vectors, Problem Statement 2A: Pathogen Biology, Virulence Determinants, and Genetics of the Pathogen. 10. Analysis of distribution of Beet Black Scorch Virus (BBSV) in U.S., and develop methods for inoculation of BBSV. BBSV, initially characterized in China, is a new member of the genus Necrovirus and was first identified in a production field in Colorado in 2005. However, BBSV infected sugarbeet plants never showed the leaf symptoms described during the initial report; therefore, inoculation of the soil was a main concern. Rabbit anti-BBSV antiserum with high sensitivity was produced from a purified preparation of the virus. A soil survey for distribution of BBSV in sugarbeet production areas within the US was conducted by ARS scientists in the Crop Improvement and Protection Research Unit in Salinas, CA, and to date all of the soil samples from sugarbeet fields were negative for BBSV. Based on extremely low incidence in the U.S., and a questionable relationship between BBSV infection and previously described symptoms from China, continuation of research on inoculation methods is no longer a priority. Research described above was conducted by the USDA-ARS Virology Lab in Salinas, and supports NP303 Component 2, Biology, Ecology, Epidemiology, and Spread of Plant Pathogens and Their Relationships with Hosts and Vectors, Problem Statement 2A: Pathogen Biology, Virulence Determinants, and Genetics of the Pathogen. 11. Genetic resistance to Cucurbit leaf crumple virus in melon. Cucurbit leaf crumple virus (CuLCrV), transmitted by Bemisia tabaci biotype B, is a begomovirus common in fall melons (Cucumis melo L.) planted from July through September in the American desert southwest. Melon breeding line MR-1, and six plant introductions (PI 124111, PI 124112, PI 179901, PI 234607, PI 313970, and PI 414723) exhibited partial resistance to CuLCrV in naturally infected field tests and controlled inoculation greenhouse tests. PI 236355 was completely resistant in two greenhouse tests, while other lines exhibited partial resistance as confirmed by PCR amplification of viral DNA. Genetic resistance to CuLCrV in melon involves a single, recessive gene. This resistance source will provide an important means of controlling this virus in an environment where other methods only slow the disease due to heavy vector pressure. This work is a collaboration between the USDA-ARS Virology and Vegetable Breeding Programs in Salinas, and the research described above is being conducted in support of NP303 Component 2, Biology, Ecology, Epidemiology, and Spread of Plant Pathogens and Their Relationships with Hosts and Vectors, Problem Statement 2A: Pathogen Biology, Virulence Determinants, and Genetics of the Pathogen. 12. Biological and molecular characterization of an American sugar beet-infecting Beet western yellows virus isolate. Three aphid-transmitted viruses belonging to the Polerovirus genus, Beet mild yellowing virus (BMYV), Beet chlorosis virus (BChV), and Beet western yellows virus (BWYV), have been described as pathogens of sugar beet. Biological and serological characterization of an American sugar beet isolate of Beet western yellows virus (BWYV-USA) suggested that BWYV-USA displayed a host range similar to that of BMYV, but distinct from those of BChV and the lettuce and rape isolates of Turnip yellows virus. The complete genomic RNA sequence of BWYV-USA showed a genetic organization and expression typical of other Polerovirus members and provided indications of genetic relationships and possible evolutionary links to other members of the Polerovirus genus. Results demonstrate that BWYV-USA is a distinct species in the Polerovirus genus, and greatly clarify the nomenclature of this important group of viruses. This research was a collaborative effort between the USDA-ARS Virology Lab in Salinas, INRA, Colmar, France, and BBSRC, Broomsbarn, UK, and supports NP303 Component 2, Biology, Ecology, Epidemiology, and Spread of Plant Pathogens and Their Relationships with Hosts and Vectors, Problem Statements 2A: Pathogen Biology, Virulence Determinants, and Genetics of the Pathogen, and 2C: Population Dynamics, Spread, and Epidemiology of Pathogens.
5.Significant Activities that Support Special Target Populations
Liu, H., Lewellen, R.T. 2008. Suppression of Resistance-breaking Beet Necrotic Yellow Vein Virus Isolates by Beet Oak-leaf Virus in Sugar Beet.. Plant Disease 92:1043-1047
Larson, R.L., Wintermantel, W.M., Hill, A.L., Fortis, L.L., Nunez, A. 2008. Proteome changes in sugar beet in response to Beet necrotic yellow vein virus. Physiological and Molecular Plant Pathology. doi:10.1016/j.pmpp.2008.04.003
Polston, J.E., Hladky, L.L., Akad, F., Wintermantel, W.M. 2008. First Report of Cucurbit Yellow Stunting Disorder Virus in Cucurbits in Florida. Plant Disease. 92:1251
Wintermantel, W.M., Hladky, L.L. 2008. Resistance to curly top viruses through virus induced gene silencing. Phytopathology. 92:S172